JP2023548890A - Coating agent for electron transport layer of reverse structure perovskite solar cell and reverse structure perovskite solar cell - Google Patents

Abstract

The present invention provides surface-modified metal oxide nanoparticles as a coating agent for forming an electron transport layer (or electron transport layer) in the form of a dispersion type coating agent, and utilizes the coating agent to transport electrons. Concerning inverted structure perovskites formed by layers.

Description

The present invention relates to a coating agent for forming an electron transport layer of a solar cell and an inverted perovskite solar cell containing an electron transport layer formed using the coating agent.

In order to solve the earth's environmental problems caused by the depletion of fossil energy and its use, research into renewable and clean alternative energy sources such as solar energy, wind power, and hydropower is actively underway.

Under these circumstances, interest in solar cells that directly convert electrical energy from sunlight is increasing significantly. Here, the solar cell refers to a battery that generates current-voltage using the photoelectric effect that absorbs light energy from sunlight and generates electrons and holes.

Currently, it is possible to manufacture n-p diode type silicon (Si) single-crystal based solar cells with a light energy conversion efficiency of over 20%, and they are actually used for solar power generation. There are also solar cells that use compound semiconductors such as gallium arsenide (GaAs). However, solar cells based on inorganic semiconductors require highly purified materials in order to achieve high efficiency, so a lot of energy is consumed in refining the raw materials, and it is difficult to use the raw materials. The process of making solar cells into single crystals or thin films requires expensive process equipment, which limits the ability to reduce the manufacturing costs of solar cells and has become an obstacle to large-scale utilization.

Therefore, in order to manufacture solar cells at low cost, it is necessary to significantly reduce the cost of the materials used as the core of solar cells or the cost of the manufacturing process. Research is underway on perovskite solar cells that can be manufactured using this process.

Recently, a perovskite solar cell that uses (NH ₃ CH ₃ )PbX ₃ (X=I, Br, Cl), a halogen compound with a perovskite structure, as a photoactive substance has been developed, and research for commercialization is underway. . The general structural formula of a perovskite structure is an ABX ₃ structure, in which an anion is located at X, a large cation is located at A, and a cation with a small size is located at B.

Perovskite solar cells, organometallic halogen compounds with the molecular formula (CH ₃ NH ₃ )PbX ₃ , were first used in photoactive materials in solar cells in 2009. Since then, solid-state perovskite solar cells with the current structure were developed in 2012, and efficiency has been rapidly improved. A typical perovskite solar cell uses a metal oxide for an electron transport layer, and mainly uses an organic material or a polymer material such as spiro-OMETAD for a hole transport layer (HTL). That is, a porous film or thin film of metal oxide is fabricated on a transparent electrode such as FTO and coated with a perovskite material, and then a hole transport layer is coated and then a metal oxide film such as gold (Au) or silver (Ag) is coated. Deposit the electrode layer.

Important issues for the commercialization of perovskite solar cells are ensuring stability and flexible technology, but the existing electron transport layer formed using metal oxide on top of the photoactive layer is After depositing or coating a metal oxide on top of the photoactive layer (or light absorbing layer), another organic binder coating layer was formed thereon. However, when metal oxides are formed by vapor deposition, the manufacturing process is complicated and multi-step, which greatly increases manufacturing costs, and there are disadvantages in that the light absorption layer may be damaged by physical and chemical energy generated during the vapor deposition process. There is. The method for forming an organic binder coating layer involves high-temperature heat treatment to form the coating layer, but perovskite materials have the problem of being decomposed at high temperatures of 200°C or higher, reducing the flexibility of solar cells. There was a problem that narrowed the application range of perovskite solar cells.

The present invention was devised to solve the above-mentioned problems, and uses a surface-modified metal oxide as a coating agent for forming an electron transport layer (or electron transport layer, ETL, Electron Transporting Layer). Nanoparticles are provided as a dispersion-type coating agent, and using this, an inverted structure perovskite with an electron transport layer formed will be provided.

In order to solve the above-mentioned problems, the present invention relates to a coating agent for an electron transport layer of an inverted structure perovskite solar cell, which includes a dispersion liquid in which a surface-modified metal oxide is dispersed in an organic solvent. .

In a preferred embodiment of the present invention, the electron transport layer coating agent of the present invention may include 0.50 to 3.00% by weight of a surface-modified metal oxide and the remaining amount of an organic solvent.

In a preferred embodiment of the present invention, the organic solvent may have a dielectric constant of 20 or less.

In a preferred embodiment of the present invention, the organic solvent may include one or more selected from isopropyl alcohol, butyl alcohol, 2-methoxyethanol, and ethyl acetate.

In a preferred embodiment of the present invention, the surface-modified metal oxide may be surface-modified by reacting metal oxide nanoparticles with a compound represented by Formula 1 below.

In the chemical formula 1, R ¹ to R ⁵ are independently hydrogen atoms or halogen atoms, and n is 0 to 5.

In a preferred embodiment of the present invention, the metal oxide nanoparticles include tin (Sn), zirconium (Zr), strontium (Sr), zinc (Zn), vanadium (V), molybdenum (Mo), and tungsten (W). ), niobium (Nb), aluminum (Al), and gallium (Ga).

In a preferred embodiment of the present invention, the metal oxide nanoparticles may have an average particle size of 2 to 10 nm.

Another object of the present invention relates to an electron transport layer of an inverted structure perovskite solar cell comprising a coating layer formed with the above-mentioned coating agent for an electron transport layer.

In a preferred embodiment of the present invention, the coating layer may have a light transmittance of 88 to 95% for a wavelength of 500 to 550 nm when the thickness is 20 to 30 nm.

Yet another object of the present invention relates to an inverted perovskite solar cell comprising the electron transport layer.

As a preferred embodiment of the present invention, the inverted structure perovskite solar cell includes a conductive substrate, a drain electrode, a hole transport layer, a light absorption layer, an electron transport layer and The structure may include a structure in which source electrodes are sequentially stacked.

In a preferred embodiment of the present invention, the inverted perovskite solar cell may further include a passivation layer between the light absorption layer and the electron transport layer.

The coating agent for forming an electron transport layer of the present invention can form an ultra-thin film with a thickness of 1 to 20 nm through low-temperature heat treatment at 200°C or less without the need for a high-temperature treatment process for forming a thin film, thereby causing damage to the perovskite light-absorbing layer. The electron transport layer formed with the coating liquid of the present invention has high thin film uniformity, is excellent in V _oc (open-circuit voltage) and FF (fill factor) of solar cells, and has a high A solar cell with excellent light transmittance (J _sc (short-circuit current)) and excellent photo-electric conversion efficiency can be manufactured.

FIG. 1 is a TEM image of SnO ₂ nanoparticles produced in Example 1.

FIG. 2 is an XRD measurement graph of SnO ₂ nanoparticles produced in Example 1.

FIG. 3 is an FT-IR measurement graph of the surface-modified SnO ₂ nanoparticles produced in Example 1.

Figure 4 (a) is a photograph of a solution in which unmodified _SnO2 nanoparticles are dispersed in isopropyl alcohol, and (b) is a photograph of the coating liquid for forming an electron transport layer produced in Example 1. This is a photo.

FIG. 5 shows the results of measuring the transmittance of a thin film manufactured using the coating liquid for forming an electron transport layer of Example 1.

FIG. 6 is a structural drawing and a cross-sectional SEM measurement image of the inverted structure perovskite solar cell manufactured in Manufacturing Example 1.

FIG. 7 shows the results of measuring the current density of the inverted structure perovskite solar cell manufactured in Production Example 1.

The present invention will be explained in more detail below.

The present invention relates to a coating agent for forming an electron transporting layer (or electron transporting layer, ETL) of an inverted structure perovskite solar cell, in which surface-modified metal oxide nanoparticles are dispersed in an organic solvent. Contains a dispersion liquid.

The coating agent of the present invention preferably contains 0.50 to 3.00% by weight of the surface-modified metal oxide and the remaining amount of an organic solvent, based on the total weight. 0.58 to 2.88% by weight of the organic solvent, more preferably 0.65 to 1.91% by weight of the surface-modified metal oxide and the remaining amount of the organic solvent.

At this time, if the content of the surface-modified metal oxide in the coating agent is less than 0.50% by weight, there is a problem that the light absorption layer is exposed during the formation of the SnO ₂ thin film because the SnO ₂ content is insufficient. If the amount exceeds 3.00% by weight, the thickness of the _SnO2 thin film may increase and the short circuit current (Jsc) and open circuit voltage (Voc) values of the solar cell may decrease. It is better to include modified metal oxides.

The organic solvent may have a dielectric constant of 20 or less, preferably 5 to 15. Specific examples of such organic solvents include isopropyl alcohol, butyl alcohol, 2-methoxyethanol, and ethyl acetate, which can be used alone or in combination as the organic solvent of the present invention. If a solvent with a dielectric constant exceeding 20 is used, there may be a problem that the attractive force between the SnO ₂ particles and the polar solvent increases, causing the SnO ₂ particles to aggregate (decreased dispersibility _and dispersion stability). There may be a problem that the perovskite material, which is the light absorption layer, is decomposed by the polar solvent during the process of forming the thin film.

The surface-modified metal oxide nanoparticles are produced in the first step of producing metal oxide nanoparticles; The particles can be manufactured by performing a process that includes two steps: manufacturing the particles.

In the chemical formula 1, R ¹ to R ⁵ are independently a hydrogen atom or a halogen atom, preferably a halogen atom, and more preferably -F. And n is 0 to 5, preferably 0 to 3, and more preferably 0 to 2.

More specifically, the first step is step 1-1 of mixing a metal precursor and ultrapure water to produce a metal precursor solution; adding a basic aqueous solution to the metal precursor solution to produce a reaction solution. and step 1-3 of performing hydrothermal synthesis on the reaction solution and obtaining metal oxide nanoparticles from the hydrothermal synthesis product.

The metal precursor solution of step 1-1 may include a metal precursor and ultrapure water, and the concentration of the metal precursor in the metal precursor solution is 0.15 to 0.7M, preferably 0. .16 to 0.5M. At this time, if the concentration of the metal precursor in the metal precursor solution is less than 0.15M, the amount of metal oxide nanoparticles obtained may be excessively small, and the concentration of the metal precursor in the metal precursor solution may be If it exceeds 0.7M, the viscosity of the metal precursor aqueous solution will increase, and the size of metal oxide nanoparticles will be non-uniform when manufactured under the same process conditions, making it impossible to obtain uniform nanoparticles. There may be a problem.

The basic aqueous solution in steps 1-2 may include at least one selected from a KOH aqueous solution, a NaOH aqueous solution, a hydrazine aqueous solution, and an NH ₄ OH aqueous solution. The amount of the basic aqueous solution to be used is such that the pH of the reaction solution is 8.0 or more, preferably about 8.0 to 9.0, more preferably about 8.2 to 8.8. If the pH is less than 8, the amount of metal oxide nanoparticles obtained may be excessively small, and the metal precursor solution will turn into a gel and cannot be stirred well. There can be problems, and if the pH is too high, there can be problems with the metal oxide particles becoming too large in size.

The hydrothermal synthesis in steps 1-3 can be performed by applying a general hydrothermal synthesis method used in the industry, and the hydrothermal synthesis is carried out at a temperature of 100 to 200°C, preferably 120 to 200°C. It is better to carry out the reaction at 190°C, more preferably at 140 to 180°C, for 6 to 48 hours, preferably for 10 to 24 hours, more preferably for 12 to 18 hours. At this time, if the hydrothermal synthesis temperature is less than 100°C, there may be a problem that the crystallinity of the metal oxide is low, and if it exceeds 200°C, there may be a problem that the size of the metal oxide particles increases. Furthermore, if the hydrothermal synthesis time is less than 6 hours, there may be a problem in which the yield of metal oxide nanoparticles is excessively reduced, and if it exceeds 48 hours, there may be a problem in which the size of the hydrothermal composite becomes excessively large. Therefore, it is better to perform hydrothermal synthesis within the above-mentioned time.

Metal oxide nanoparticles obtained through hydrothermal synthesis can be repeatedly washed 3 to 5 times using ultrapure water and ethanol.

The metal oxide nanoparticles thus obtained may have an average particle size of 2 to 10 nm, preferably 2 to 8 nm, more preferably 3 to 5 nm.

Further, the metal oxides of the metal oxide nanoparticles include tin (Sn), titanium (Ti), zinc (Zn), cerium (Ce), zirconium (Zr), strontium (Sr), zinc (Zn), and vanadium. (V), molybdenum (Mo), tungsten (W), niobium (Nb), aluminum (Al), and gallium (Ga). In one embodiment, the metal oxide may include SnO ₂ , TiO ₂ , ZnO, CeO ₂ and/or Zn ₂ SnO ₄ , and preferably includes SnO ₂ and/or ZnO. .

Next, the second step is a step of modifying the surface of the metal oxide nanoparticles obtained in the first step, and the step 2-1 is to mix the metal oxide nanoparticles and ultrapure water to prepare a solution. step 2-2 of adding the compound represented by the chemical formula 1 to the solution to produce a reaction solution; step 2-3 of performing a reflux reaction on the reaction solution; performing a reflux reaction to remove a reaction product from the solution. performing a process including steps 2-4 of separating and washing the separated reaction product; and steps 2-5 of drying the washed reaction product to obtain surface-modified metal oxide nanoparticles; Can be done.

The reaction solution may contain 100 to 700 parts by weight of ultrapure water and 300 to 1,500 parts by weight of the compound represented by Formula 1 based on 100 parts by weight of the metal oxide nanoparticles. It may contain 350 to 600 parts by weight of ultrapure water and 400 to 1,200 parts by weight of the compound, more preferably 350 to 550 parts by weight of ultrapure water and 450 parts by weight of the compound, based on 100 parts by weight of the oxide nanoparticles. ~850 parts by weight. At this time, if the amount of ultrapure water used is less than 100 parts by weight, there may be a problem that the solvent will not be refluxed sufficiently during the surface modification process and the surface modification will not be uniformly performed. If it exceeds , there may be a problem that the reflux reaction time becomes excessively long. Furthermore, if the amount of the compound used is less than 300 parts by weight, the degree of modification of the surface of the metal oxide may be excessively insufficient or uneven, leading to the problem that the metal oxide particles are not uniformly dispersed in the solvent and are precipitated. However, if it exceeds 1,500 parts by weight, it is uneconomical, and there may be a problem that the device characteristics of the solar cell are deteriorated due to unreacted compounds, so it is better to use it within the above range.

The reflux reaction in the 2-3 stages can be carried out at 80 to 140°C, preferably 80 to 120°C. At this time, if the reflux reaction temperature is less than 80°C, reflux is not sufficiently carried out. If the temperature exceeds 140° C., the surface of the metal oxide may be excessively modified, which may impede the operation of the solar cell element. The appropriate reflux reaction time is about 1 to 4 hours, preferably about 1.5 to 3 hours.

The 2-4 steps of separation and/or washing can be performed by common methods used in the industry, and in one embodiment, after centrifugation is performed to collect the refluxed reaction product from the reaction solution. This can be done by washing with ultrapure water or the like.

The drying steps 2 to 5 can be performed by a general method used in the industry, and in one embodiment, the reaction product obtained by washing is heated in an oven at 50 to 80°C. It can be carried out.

The above-mentioned coating agent for forming an electron transport layer of the present invention can be used in general methods such as spin coating, blade coating, bar coating, spray coating, gravure coating, and die coating. The coating can be performed by a coating method, and in one embodiment, after coating, heat treatment is performed at 200° C. or less to a thickness of 100 nm or less, preferably a thickness of 1 to 40 nm, more preferably a thickness of 1 to 20 nm. An ultra-thin film may be formed.

An inverted or pin structure perovskite solar cell can be manufactured as follows using the coating agent of the present invention.

The inverted structure perovskite solar cell of the present invention comprises a conductive substrate, a drain electrode, a hole transport layer (HTL), a light absorption layer (or photoactive layer), an electron transport layer (or electron transport layer) , ETL, Electron
A solar cell may have a structure in which a transporting layer and a source electrode are stacked in order.

Further, in the inverted structure perovskite solar cell of the present invention, a conductive substrate, a drain electrode, a hole transport layer, a light absorption layer, an electron transport layer, and a source electrode are laminated in this order to constitute one set, and the above-mentioned The set may be formed by laminating a single layer or multiple layers.

The conductive substrate may be a general conductive substrate used in the industry, for example, made of a material such as polyethylene terephthalate, polyethylene naphthalate, polyester sulfone, aromatic polyester, or polyimide. A transparent plastic substrate, a glass substrate, a tin substrate, a silicon substrate, etc. can be used.

The drain electrode may be made of a material containing at least one selected from a conductive metal, a conductive metal alloy, a metal oxide, and a conductive polymer, and a preferable example is ITO (Induim Tin Oxide). ), FTO (Fluorine doped Tin
ZTO:Ga (gallium doped) ZTO) _, IGZO (lndium gallium zinc oxide), IZO ( _lndium doped zinc oxide) and/or AZO (aluminum doped zinc oxide).

The hole transport layer (HTL) may include an inorganic and/or organic hole transport material. The inorganic hole transport material may include one or more selected from nickel oxide (NiO _x ), CuSCN, CuCrO ₂ , and CuI.

The organic hole transmitting substances include carbazole derivatives, polyarylalkane derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styryl anthracene derivatives, fluorene derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, and aromatic tertiary derivatives. Amine compounds, styrylamine compounds, aromatic dimethylidine compounds, porphyrin compounds, phthalocyanine compounds, polythiophene derivatives, polypyrrole derivatives, polyparaphenylene vinylene derivatives, pentacene, coumarin 6, 3-(2-benzothiazolyl) )-7-(diethylamina)coumarin), ZnPC (zincphthalocyanine), CuPC (copper phthalocyanine), TiOPC (titanium oxide phthalocyanine) , Spiro-MeOTAD (2,2',7,7'-tetrakis(N,N-p- dimethoxyphenylamino)-9,9'-spirobifluorene), F16CuPC(copper(II)1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro -29H,31H-phthalocyanine), SubPc (boron subphthalocyanine chloride) and N3 (cis-di(thiocyanato)-bis(2,2'bipyridyl-4,4'-dicarboxyl) ic acid)-ruthenium(II), P3HT(poly[ 3-hexylthiophene]), MDMO-PPV (poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)]-1,4-phenylene vinylene), MEH-PPV (poly[2-methoxy-5- ( 2”-ethylhexyloxy)-p-phenylene vinylene], P3OT (poly (3-octyl thiophene)), POT (poly (octyl thiophene)), P3DT (poly (3-decyl thiophene)) ene)), P3DDT(poly(3-dodecyl thiophene), PPV (poly(p-phenylene vinylene)), TFB(poly(9,9'-dioctylfluorene-co-N-(4-butylphenyl)diphenyl amine), polyaniline (Polyaniline) ine), Spiro-MeOTAD ([2, 22',7,77'-tetrkis (N,N-di-pmethoxyphenyl ami
ne)-9,9,9'-spirobi fluorine]), CuSCN, Cul,
PCPDTBT(Poly"2,1,3-benzothiadiazole-4,7-diyl"4,4-bis(2-ethylhexyl-4H-cyclopenta "2,1-b:3,4-b'" dithiophene-2,6 -diyl)", Si-PCPDTBT(poly[(4,4'-bis(2-ethylhexyl) dithi
eno[3,2-b:2',3'-d]silole)2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl]), PBDTTPD(poly((4 ,8-diethylhexyloxyl), PFDTBT(poly"2,7-(9-(2-ethylhexyl)-9-hexyl-fluorene)-alt-5,5-(4',7,-di-2-thienyl-2 ',1',3'-benzothiadiazole)'), PFO-DBT(poly[2,7-9,9-(dioctyl-fluorene)-alt-5,5-(4',7'-di-2- thienyl-2',1',3'-benzothiadiazole)]), PSiFDTBT(poly'(2,7-dioctylsilafluorene)-2,7-diyl-alt-(4,7-bis(2-thienyl)-2, 1,3-benzot
hiadiazole)-5,5'-diyl"), PCDTBT(Poly""9-
(1-octylnonyl)-9H-carbazole-2,7-diyl"-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl"), PFB (poly (9 ,9'-dioctylfluorene-co-bis(N,N'-(4,butylpheny))bis(N,N'-phenyl-1,4-phenylene)diamin
e), F8BT(poly(9,9'-dioctylfluorene-cobenz
othiadiazole), PEDOT(poly(3,4-ethylenedioxythiophene)), PEDOT:PSS poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate), PTAA (poly(triarylamine)), 2-PACz, and/or MeO-2PACz can be included.

Examples of the method for forming the hole transport layer include a coating method and a vacuum evaporation method. Examples of the coating method include a gravure coating method, a bar coating method, a printing method, a spray method, a spin coating method, a dipping method, and the like. Examples include die coating method.

In addition, in the structure of the solar cell of the present invention, the light absorption layer may include a general perovskite material applied to a light absorption layer of a solar cell, and a preferable example is a perovskite material represented by the following chemical formula 2. Can contain substances.

In Formula 2, C is a monovalent cation, which may include amines, ammonium, Group 1 metals, Group 2 metals, and/or other cations or cation-like compounds, preferably formamide. formamidinium (FA), methylammonium (MA), FAMA, CsFAMA or N(R) ₄ ⁺ (wherein R may be the same or different groups, R is , a straight-chain alkyl group having 1 or more carbon atoms, a branched-chain alkyl group having 3 to 5 carbon atoms, a phenyl group, an alkylphenyl group, an alkoxyphenyl group, or an alkyl halide).

Moreover, M in chemical formula 2 is a divalent cation, and includes Fe, Co, Ni, Cu, Sn, Pb,
It can contain one or two selected from Bi, Ge, Ti, Eu, and Zr.

Further, X in chemical formula 2 is a monovalent anion, and may contain one or more halide elements selected from F, Cl, Br, and I and/or a group 16 anion; a preferable example is , X may be 1 _x Br _3x (O≦x≦3).

As a preferred embodiment of the chemical formula 2, FAPbI _x Br _3x (O≦x≦3), MAPbl _x Br _3-x (O≦x≦3), CSMA FAPbl _x Br _3-x (O≦x≦3) ), _CH3NH3PbX3 (X=Cl, Br, _I , _{Brl2 or Br2I} ), _CH3NH3SnX3 (X=Cl, Br _or I), CH( ₌ NH _{) NH3PbX3} (X=Cl, Br, I, Brl ₂ or Br ₂ I), CH(=NH)NH ₃ SnX ₃ (X=Cl, Br or I), and the like.

Furthermore, in the solar cell of the present invention, the light absorption layer may be a single layer made of the same perovskite material, or a multilayer structure in which many layers made of other perovskite materials are laminated. Often, a light absorption layer made of one type of perovskite material contains the one type of perovskite material and another different type of perovskite material, which has a filler shape such as a columnar shape, a plate shape, a needle shape, a wire shape, or a rod shape. But that's fine.

Among the components of the solar cell of the present invention, the electron transport layer is coated with a coating solution of the above-mentioned coating agent of the present invention (a dispersion of surface-modified metal oxide nanoparticles dispersed in an organic solvent). The electron transport layer may be formed on the light absorption layer by performing a low temperature heat treatment at 200° C. or lower, preferably 30 to 100° C. or lower to form a coating layer in the form of a thin film.

At this time, the coating may be spin coating, blade coating, bar coating, spray coating, gravure coating, or die coating.

It is preferable that the electron transport layer has a thickness of 100 nm or less, preferably 1 to 40 nm, more preferably 1 to 20 nm; in this case, if the thickness of the electron transport layer exceeds 100 nm, Since there may be a problem that the short circuit current (J _sc ) and open circuit voltage (V _oc ) of the solar cell decrease, it is better to form the layer with a thickness within the above range.

The surface of the coating layer thus formed, that is, the electron transport layer, may have a very low roughness, with an RMS (root mean square) roughness of 30 nm or less, preferably 17.0 to 17.0 nm. 25.0 nm, more preferably 17.5 to 24.0 nm.

In the configuration of the solar cell of the present invention, the source electrode is made of one selected from Pt, Au, Ni, Cu, Ag, In, Ru, Pd, Rh, Ir, Os, C, and a conductive polymer. It can be formed by coating or depositing more than one material.

In addition, the solar cell of the present invention may further include a passivation layer between the light absorption layer and the electron transport layer.

Hereinafter, the present invention will be explained in more detail through examples, but the following examples are not intended to limit the scope of the present invention, and should be interpreted as helping the understanding of the present invention.

<Example 1>

Example 1: Production of coating liquid for forming electron transport layer (ETL)

(1) Production of _SnO2 nanoparticles

_SnCl4.5H2O was put into a beaker containing ultrapure water and stirred to produce a metal precursor solution with a _SnCl4 concentration of 0.33M, and then a basic aqueous solution was added to 265 ml of the metal precursor solution _. 35 ml of NH ₄ OH was added to prepare a reaction solution with an aqueous pH of about 8.0-8.5.

The reactive solution was placed in a pressure vessel (autoclave or hydrothermal reactor), and hydrothermal synthesis was performed at 180° C. for 12 hours.

Next, the material obtained through hydrothermal synthesis was washed 3 to 5 times using ultrapure water and ethanol to prepare SnO ₂ nanoparticles.

The average particle size of the SnO ₂ nanoparticles produced was 3-5 nm.

A TEM measurement image of the manufactured SnO ₂ nanoparticles is shown in FIG. 1, and an XRD measurement result is shown in FIG.

(2) Production of surface-modified _SnO2 nanoparticles

8 g of the previously prepared SnO ₂ nanoparticles were added to a round bottom flask containing 40 mL of ultrapure water and stirred, and then 54 g of TFA (trifluoroacetic acid) was added to prepare a reaction solution. A condenser was attached to a round bottom flask containing the prepared reaction solution, and a reflux reaction was carried out at 90° C. for 2 hours.

Next, nanoparticles were separated from the refluxed reaction solution using a centrifuge, and then dried in an oven at 60° C. to produce surface-modified SnO ₂ nanoparticles.

FIG. 3 shows the results of FT-IR measurement of the surface-modified SnO ₂ nanoparticles produced.

(3) Production of a dispersion solution (coating solution) of surface-modified _SnO2 nanoparticles

After adding 30 mg of the previously prepared surface-modified _SnO2 nanoparticles to 4 ml of isopropyl alcohol with low polarity (dielectric constant ≦20), a dispersion solution type electron was added using an ultrasonic grinder. A coating liquid for forming a transmission layer (approximately 0.74% by weight of surface-modified metal oxide) was produced.

Figure 4(b) shows a photograph of the dispersion type coating liquid for forming an electron transport layer, and Figure 4(a) shows 30 mg of _SnO2 nanoparticles that were not surface modified in isopropyl alcohol. This is a photograph taken after the addition and dispersion using an ultrasonic pulverizer.

<Comparative example 1>

The SnO ₂ nanoparticles prepared in (1) of Example 1 were prepared without a surface modification process.

After adding 30 mg of the SnO ₂ nanoparticles whose surface was not moisturized to 4 ml of isopropyl alcohol, a dispersion type coating solution for forming an electron transport layer was prepared using an ultrasonic grinder. A photograph of the produced coating liquid is shown in FIG. 4(a).

<Example 2, Example 3 and Comparative Example 2, Comparative Example 3>

A coating solution for forming an electron transport layer was prepared in the same manner as in Example 1, but after preparing surface-modified SnO ₂ nanoparticles having the composition shown in Table 1 below, surface-modified SnO ₂ nanoparticles were prepared. After mixing the particles with an organic solvent, a dispersion solution type coating solution for forming an electron transport layer was prepared using an ultrasonic pulverizer, and Examples 2 and 3 and Comparative Examples 2 and 3 were carried out. .

<Comparative example 4>

A coating solution for forming an electron transport layer is prepared in the same manner as in Example 1, except that the surface-modified _SnO2 nanoparticles of Example 1 are mixed with ethyl alcohol having a dielectric constant of 25, and then subjected to an ultrasonic pulverizer. Comparative Example 4 was conducted using a dispersion solution type coating solution for forming an electron transport layer.

Experimental example 1: Production of ultra-thin film and measurement of surface roughness and light transmittance of coating layer

Each of the coating solutions prepared in the Examples and Comparative Examples was spin-coated on a glass substrate and a perovskite thin film including a glass substrate, and then heat-treated at 30° C. to prepare an ultra-thin film with a thickness of 20 nm.

Then, after measuring the surface roughness of the ultra-thin film formed on the top of the perovskite thin film including the glass substrate using a non-contact method, the roughness is calculated by the root-mean-square (rms), and an arbitrary value is determined. After measuring the surface roughness at 3 points, the average value of the surface roughness at the 3 points is shown in Table 2 below.

In addition, the ultra-thin film formed on a glass substrate was scanned with near-infrared rays on the substrate on which the ultra-thin film was formed using a UV spectrum measurement method to measure the absorbance and light transmittance (%) of the sample. The results are shown in Table 2 below, and the light transmittance measurement results for Example 1 are shown in FIG. At this time, the light transmittance is the light transmittance at 500 to 550 nm.

The RMS roughness and light transmission in Table 2 show that Examples 1 to 3 have a very low RMS roughness of 18.0 to 23.0 nm and an excellent light transmittance of 90% or more. It was confirmed that the material had excellent optical properties. On the other hand, the coating liquid using surface-modified SnO ₂ nanoparticles was prepared by using only 270 parts by weight of TFA, which is less than 300 parts by weight, during the synthesis of the surface-modified SnO ₂ nanoparticles. In the case of Example 2, when compared with Example 1 or Example 2, there was a problem that not only the light transmittance was low but also the roughness was relatively excessively high. In the case of Comparative Example 3 using parts by weight, when compared with Example 3, the roughness increased and the light transmittance decreased in some areas, but this was due to surface-modified SnO ₂ nanoparticles. This is thought to be due to a phenomenon in which some of the nanoparticles solidify.

In the case of Comparative Example 4, there was a problem in that the SnO ₂ nanoparticles were not dispersed but aggregated and coated on the upper end of the glass substrate in the form of islands, so that a thin film was not formed.

Production Example 1: Production of a reverse structure perovskite solar cell to which surface-modified _SnO2 nanoparticles are applied

As a drain electrode, an organic substrate (1.1 mm thick, 15.0 Ω/sq) coated with indium tin oxide (ITO) to a thickness of about 110 nm was prepared using acetone and isopropyl alcohol (ITO).
Opropyl alcohol (IPA) was sequentially used for 1 hour at a time using an ultrasonic cleaner.

Next, a 30 nm thick hole transport layer (NiO _x ) was formed on the ITO substrate using E-beam vacuum deposition conditions.

Next, a yellow light absorption layer solution prepared by dissolving dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) was formed on the hole transport layer by spin coating, and the layer was coated at 100° C. for 20 minutes. By heat treatment, a NiOx hole transport layer and a light absorption layer (CSMAFAPbl _x Br _3-x (0≦x≦3)) having a perovskite crystal structure with a thickness of 450 to 500 nm were formed.

Next, a 13 nm thick passivation layer (C ₆₀ fullerene) was formed on the light absorption layer using thermal evaporation method conditions.

Next, the surface-modified coating solution prepared in Example 1 was spin-coated on the passivation layer at 1,500 rpm for 1 minute, and then heat-treated at 30° C. to form an electron transport layer with a thickness of 20 nm. formed.

Next, a perovskite solar cell with an inverted structure was fabricated by depositing silver (Ag) on the electron transport layer to a thickness of 150 nm at a pressure of 1×10 ⁻⁸ torr to form a source electrode.

FIG. 6 shows an SEM measurement image of the manufactured solar cell.

Production Example 2, Production Example 3, and Comparative Production Examples 1 to 3

A perovskite solar cell with an inverted structure was manufactured by the same method as in Production Example 1, but each of the coating agents of Examples 2, 3, and Comparative Examples 1 to 3 was used instead of the coating agent of Example 1. Production examples 2, 3, and comparative production examples 1 to 3 were conducted by producing solar cells each having an electron transport layer formed thereon.

Experimental example 2: Performance measurement of solar cells

The current-voltage characteristics and efficiency of the solar cell manufactured in Manufacturing Example 1 were measured, and the results are shown in Table 3 below. The measurement results of short circuit current density for Manufacturing Example 1 are shown in FIG.

The current-voltage characteristics and efficiency measurement results of the solar cell shown in Table 3 and FIG. 7 show that the solar cell has a very high fill factor and photoelectric conversion efficiency.

Claims (11)

A coating agent for an electron transport layer of an inverted perovskite solar cell, comprising a dispersion in which a surface-modified metal oxide is dispersed in an organic solvent, the organic solvent having a dielectric constant of 20 or less. . The coating agent for an electron transport layer of an inverted perovskite solar cell according to claim 1, comprising 0.50 to 3.00% by weight of a surface-modified metal oxide and the remaining amount of an organic solvent. 2. The electron transport layer of an inverted perovskite solar cell according to claim 1, wherein the organic solvent contains one or more selected from isopropyl alcohol, butyl alcohol, 2-methoxyethanol, and ethyl acetate. Coating agent. The inverted structure perovskite solar according to claim 1, wherein the surface-modified metal oxide is surface-modified by reacting metal oxide nanoparticles with a compound represented by the following chemical formula 1. Coating agent for the electron transport layer of batteries.

(In the chemical formula 1, R ¹ to R ⁵ are independently hydrogen atoms or halogen atoms, and n is 0 to 5.) The metal oxide nanoparticles include tin (Sn), zirconium (Zr), strontium (Sr), zinc (Zn), vanadium (V), molybdenum (Mo), tungsten (W), niobium (Nb), aluminum ( The coating agent for an electron transport layer of an inverted structure perovskite solar cell according to claim 4, characterized in that it contains a metal oxide containing one or more selected from Al) and gallium (Ga). . The coating agent for an electron transport layer of an inverted structure perovskite solar cell according to claim 4, wherein the metal oxide nanoparticles have an average particle size of 2 to 10 nm. An electron transport layer for an inverted perovskite solar cell, comprising a coating layer formed from the coating agent according to any one of claims 1 to 6. The inverted structure perovskite solar cell according to claim 7, wherein the coating layer has a light transmittance of 88 to 95% for a wavelength of 500 to 550 nm when the thickness is 20 to 30 nm. electron transport layer. An inverted perovskite solar cell comprising the electron transport layer according to claim 7. conductive substrate, drain electrode, hole transport layer
The inverted structure perovskite solar cell according to claim 9, characterized in that the inverted structure perovskite solar cell includes a structure in which a transport layer, a light absorption layer, an electron transport layer, and a source electrode are sequentially stacked. The inverted perovskite solar cell of claim 10, further comprising a passivation layer between the light absorption layer and the electron transport layer.